remove mentioning of Exp and Identity in test_utils.jl

Author: torfjelde

src/test_utils.jl

@@ -686,7 +686,7 @@ Simple model for which [`default_transformation`](@ref) returns a [`StaticTransf
 end
 
 function DynamicPPL.default_transformation(::Model{typeof(demo_static_transformation)})
-    b = Bijectors.stack(Bijectors.Exp(), Bijectors.Identity())
+    b = Bijectors.stack(exp, identity)
     return DynamicPPL.StaticTransformation(b)
 end